The metal and heat treatment of the
Krag
was the same as that of the SHT M1903; it was simply carried over from the old rifle production to the new.
A couple of factors reduce the chance of a Krag action failing. One has been mentioned, the fully enclosed case head possible with a rimmed cartridge. Another is that the Krag operates at much lower pressures, and yet another is that Krags were not made under the kind of wartime pressure in effect at Springfield in the 1917-1918 time frame.
I have fired many Krags, and only saw one blow. The case we removed from the chamber had the headstamp of a
German
7.9 s.S round. We never learned how the shooter managed to get the round into the chamber, or if he somehow resized the case. But the rifle let go, breaking the single locking lug and spreading and cracking the receiver.
Yes, the Krag does have a safety lug, the rear of the guide rib. On the
Norwegian
and
Danish
Krags, that lug bears so the rifle is a much stronger dual lug system. But on the U.S. Krag, that lug (for reasons unknown to me) was made to not bear and act only as a safety lug in case the front lug failed.
Jim